An engine may burn gaseous fuels such as hydrogen (H2), natural gas, lighter flammable hydrocarbon derivatives, etc. Using gaseous fuel in an internal combustion engine can provide various advantages compared to liquid fuel injection. Examples of such advantages may include reduction of exhaust emissions of nitrogen oxides, particulate matter, and hydrocarbons as well as increased fuel renewability and transferability.
In the example of hydrogen fueled engines, the hydrogen may be exposed to hot residual gases as well as heated engine components, such as the intake manifold. The gas may also be exposed to heat from the cylinder head porting, piston, valves, and walls of a combustion chamber during the intake stroke. This exposure can increase a propensity of the fuel to backfire, pre-ignite, and/or backflash, as well as reduce engine output. Further, such effects can be exacerbated if the hydrogen injection duration is extended.
One approach to address some issues of gaseous fuel delivery is to directly inject the gaseous fuel into the combustion chamber and then induct air after the completion of fuel injection. Specifically, JP 63-198,762 describes a method of directly injecting hydrogen into a combustion chamber. In the '762 reference, it appears that the exhaust valve is closed very near, if not at, top dead center of piston position when an exhaust stroke is completed. Further, the hydrogen injection valve is opened immediately after this exhaust valve is closed to inject hydrogen gas into a combustion chamber. Next, after the hydrogen injection valve is closed at the rotation position of the crank angle of about 90 degrees, the suction (intake) valve is opened, and supercharged air is fed to the combustion chamber and mixed with hydrogen. Then, the mixture is compressed and ignited.
However, the inventors herein have recognized that backfiring, pre-ignition, and backflash may still occur. For example, injected hydrogen may be exposed to hot combustion chamber surfaces because the hydrogen is injected at top dead center immediately after the completion of an exhaust stroke. Further, a propensity of combustion anomalies such as backfiring, pre-ignition, and/or backflash may increase when the heated hydrogen is mixed with heated boosted air inducted into the combustion chamber.
Therefore, in one embodiment, at least some of such issues may be addressed by a method for a hydrogen fueled internal combustion engine, the engine also including a combustion chamber, an intake manifold, an exhaust manifold, at least one intake valve, at least one exhaust valve, a hydrogen injector, and a compression device. The method comprises compressing air using the compression device; injecting hydrogen and mixing at least said hydrogen with air discharged from the compression device; and opening the intake valve to induct at least air into the combustion chamber, wherein the intake valve opening time varies with an operating condition. The operation condition may include one or more of temperature, speed, and load of engine that each may provide an indication of a tendency of backfiring, pre-ignition, and/or backflash.
In this way, engine efficiency may be improved by reducing backfiring, pre-ignition, and backflash. For example, in one embodiment, under conditions when backfiring, pre-ignition and/or backflash are more likely (e.g. high temperature), intake valve opening can be retarded to provide additional time before the hydrogen and/or air is inducted into the cylinder. This allows metal surfaces of the combustion chamber including the head porting more time to cool. Additionally, after the exhaust valve closes and before the intake valve opens, the downward piston motion of the intake stroke expands the combustion chamber content until the intake valve opens. This expansion may result in lower gas pressure and temperature, and thus a cooler environment for the hydrogen/air mixture to enter when the intake valve finally opens. However, under conditions where such cooling is not needed, intake valve opening may be less retarded or may be kept near the top dead center thereby to reduce any pumping losses.
Further, any reduction in torque and power due to volumetric efficiency by the late intake valve opening (and potentially late intake valve closing) can be compensated by the boosting of the intake air.
According to another aspect, a method is provided for a hydrogen fueled internal combustion engine, the engine also including a combustion chamber, an intake manifold, an exhaust manifold, at least one intake valve, at least one exhaust valve, a hydrogen injector, and a compression device. The method comprises compressing air using the compression device; injecting hydrogen and mixing at least said hydrogen with air discharged from the compression device; and opening the intake valve to induct a mixture of at least hydrogen and air into the combustion chamber wherein the intake valve opening time varies with a first operating condition; and varying the exhaust valve closing time with a second operating condition. In one embodiment, the exhaust valve closing time is advanced with respect to the top dead center when the engine speed is low. In another embodiment, the exhaust valve closing is retarded with respect to the top dead center when the engine speed is high. Further still, such adjustment can be combined in yet another embodiment.
Again, such operation can provide various advantages. For example, at low engine speed, the late intake valve opening and the early exhaust valve closing may increase fuel efficiency compared with varying the intake valve timing alone. At high engine speed, the late intake valve opening and the late exhaust valve closing may also reduce a tendency for combustion anomalies by reducing exhaust residuals.
Note that various intake and exhaust valve configurations may be used, such as electrically actuated valves, variable camshaft phasing, cam lobe switching, multiple intake valves, multiple exhaust valves, and combinations thereof. Also, note that injecting hydrogen may include injecting pure hydrogen or mixture of hydrogen and gaseous fuel such as natural gas, for example. Additionally, hydrogen may be mixed with other gases besides air. For example, hydrogen may be mixed with air and recirculated exhaust gas.